This invention relates to the joining of components by butt welding. It is known to generate the required heat for butt welding by the passage of electric current between the parts to be welded. One process employing such electric heating is resistance butt welding and another is flash butt welding, which employs a combination of arc and resistance heating. The arcs are formed when the initial points of contact between two components to be welded become molten and the molten bridge then ruptures.
Another form of butt welding, known as arc butt welding, is described in British Specification No. 1,089,178. In this specification, it was proposed, for the joining of the end faces of two tubes, to create a magnetic field such that an arc struck between the surfaces to be welded would travel round in a ring between the annular end faces. However, we have found that there is a limitation on the wall thickness of tube that can be satisfactorily welded with this technique; the maximum thickness appears to be in the range of 4 to 5 millimeters and the limitation results from the finite width of the arc.
To overcome this problem, it was proposed in British Patent Specification No. 1,475,450 that for welding tubular workpieces a central conductor should be placed within the workpieces during welding with a rotating arc, the central conductor carrying a current which, according to its direction of flow, causes the rotating arc to move outward from the axis of the tubes or inward towards this axis. This movement results from the interaction between the magnetic field generated by the current passing through the central conductor and the magnetic field around the rotating arc.
However, it is not always possible to use a central conductor within the tubes during their welding and we have devised a method of rendering more uniform the heat distribution over the faces of tubes during arc butt welding which does not involve a central conductor; moreover, this method is also applicable to the arc butt welding of non-tubular components.